MOTOR CHARACTERISTICS
p = Number of poles.
b = Number of paths in parallel on armature.
A = Area cross section magnetic circuit at air gap.
Z = Length magnetic circuit.
M = Equivalent permeability magnetic circuit.
P = Power delivered to the shaft of motor expressed in
watts.
From the experimental definition of the volt:
(1)
(2)
(3)
(4)
(5)
(6)
 
or
60 X 1086
60 X 1086e
V =
but if leakage and armature reaction be neglected,
Substituting
V =
47.7 X lQ*bel
e = E - I(Ra + R/}
47.7 X
but
therefore
V =
NapNfIAfJi
As all factors in the right-hand side of Eq. (6) are either constants
of the design or dependent upon current, a series of assumed
values of current will give corresponding values of speed (F)
from which the speed characteristic may be plotted. It will
be seen from Eq. (2) that if (<£) be constant because of field
saturation, the speed (7) will vary directly with the counter
emf. (e). Since, however, the voltage drop due to resistance is
a small percentage of the impressed voltage, it may be said that
the speed of a series motor varies with the voltage impressed xipon
it if load conditions remain the same. This fact is of importance
in the design of car control systems.
With reference to the torque characteristic and neglecting iron
losses,
P - el	(7)
2irVT X 746
P =
33000
whence
T «
X 746 X 60 X 1086<?
or
T = ""'
W8b
(8)
(9)
(10)